From: syzbot <syzbot+e8aac527b30cc7380cf3@syzkaller.appspotmail.com>
To: cgroups@vger.kernel.org, hannes@cmpxchg.org,
linux-kernel@vger.kernel.org, mkoutny@suse.com,
syzkaller-bugs@googlegroups.com, tj@kernel.org
Subject: [syzbot] [cgroups?] possible deadlock in _task_rq_lock
Date: Sat, 01 Aug 2026 17:07:42 -0700 [thread overview]
Message-ID: <6a6e8a4e.2d659fcc.1d46f5.01c7.GAE@google.com> (raw)
Hello,
syzbot found the following issue on:
HEAD commit: 8ba098e6b6ff Merge tag 'v7.2-rc5-smb3-client-fixes' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=109cd499580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f221a1b5d497ed15
dashboard link: https://syzkaller.appspot.com/bug?extid=e8aac527b30cc7380cf3
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-8ba098e6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/068ab6124703/vmlinux-8ba098e6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4658fabc1ddc/bzImage-8ba098e6.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e8aac527b30cc7380cf3@syzkaller.appspotmail.com
------------[ cut here ]------------
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
migration/0/19 is trying to acquire lock:
ffffffff8eaf3f60 (console_owner){....}-{0:0}, at: console_trylock_spinning kernel/printk/printk.c:2026 [inline]
ffffffff8eaf3f60 (console_owner){....}-{0:0}, at: vprintk_emit+0x4c0/0x6b0 kernel/printk/printk.c:2478
but task is already holding lock:
ffff88802b23b660 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:675 [inline]
ffff88802b23b660 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x88/0x140 kernel/sched/core.c:659
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #4 (&rq->__lock){-.-.}-{2:2}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
_raw_spin_lock_nested+0x31/0x40 kernel/locking/spinlock.c:382
raw_spin_rq_lock_nested+0x2c/0x140 kernel/sched/core.c:667
raw_spin_rq_lock kernel/sched/sched.h:1653 [inline]
_task_rq_lock+0xcf/0x500 kernel/sched/core.c:762
cgroup_move_task+0x81/0x320 kernel/sched/psi.c:1170
css_set_move_task+0x285/0x600 kernel/cgroup/cgroup.c:925
cgroup_post_fork+0x1f9/0x9a0 kernel/cgroup/cgroup.c:6988
copy_process+0x6b7a/0x8030 kernel/fork.c:2550
kernel_clone+0x176/0x9d0 kernel/fork.c:2748
user_mode_thread+0xcc/0x110 kernel/fork.c:2824
rest_init+0x21/0x260 init/main.c:682
start_kernel+0x48e/0x490 init/main.c:1175
x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
x86_64_start_kernel+0x12b/0x130 arch/x86/kernel/head64.c:291
common_startup_64+0x13e/0x158
-> #3 (&p->pi_lock){-.-.}-{2:2}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
_raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:166
class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:571 [inline]
try_to_wake_up+0xbd/0x1c90 kernel/sched/core.c:4292
__wake_up_common+0x135/0x1f0 kernel/sched/wait.c:108
__wake_up_common_lock kernel/sched/wait.c:125 [inline]
__wake_up+0x31/0x60 kernel/sched/wait.c:146
tty_port_default_wakeup+0x47/0x60 drivers/tty/tty_port.c:67
serial8250_tx_chars+0x68f/0x860 drivers/tty/serial/8250/8250_port.c:1723
serial8250_handle_irq_locked+0x770/0x9a0 drivers/tty/serial/8250/8250_port.c:1837
serial8250_handle_irq.part.0+0xb4/0x530 drivers/tty/serial/8250/8250_port.c:1853
serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1849 [inline]
serial8250_default_handle_irq+0xc2/0x280 drivers/tty/serial/8250/8250_port.c:1867
serial8250_interrupt+0xf8/0x1b0 drivers/tty/serial/8250/8250_core.c:86
__handle_irq_event_percpu+0x232/0x880 kernel/irq/handle.c:209
handle_irq_event_percpu kernel/irq/handle.c:246 [inline]
handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:263
handle_edge_irq+0x34c/0x950 kernel/irq/chip.c:859
generic_handle_irq_desc include/linux/irqdesc.h:188 [inline]
handle_irq arch/x86/kernel/irq.c:209 [inline]
call_irq_handler arch/x86/kernel/irq.c:265 [inline]
__common_interrupt+0xd8/0x2f0 arch/x86/kernel/irq.c:280
common_interrupt+0xb9/0xe0 arch/x86/kernel/irq.c:273
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:665
native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
arch_safe_halt arch/x86/include/asm/paravirt.h:62 [inline]
default_idle+0x9/0x10 arch/x86/kernel/process.c:768
default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:199 [inline]
do_idle+0x3a7/0x5b0 kernel/sched/idle.c:355
cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:454
start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
common_startup_64+0x13e/0x158
-> #2 (&tty->write_wait){-...}-{3:3}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
_raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:166
__wake_up_common_lock kernel/sched/wait.c:124 [inline]
__wake_up+0x1c/0x60 kernel/sched/wait.c:146
tty_port_default_wakeup+0x47/0x60 drivers/tty/tty_port.c:67
serial8250_tx_chars+0x68f/0x860 drivers/tty/serial/8250/8250_port.c:1723
__start_tx+0x3e4/0x490 drivers/tty/serial/8250/8250_port.c:1430
serial8250_start_tx+0x368/0x540 drivers/tty/serial/8250/8250_port.c:1539
__uart_start+0x295/0x510 drivers/tty/serial/serial_core.c:161
uart_write+0x211/0xb20 drivers/tty/serial/serial_core.c:629
process_output_block drivers/tty/n_tty.c:557 [inline]
n_tty_write+0x431/0x1160 drivers/tty/n_tty.c:2366
iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
file_tty_write.isra.0+0x4d2/0x890 drivers/tty/tty_io.c:1081
tty_write drivers/tty/tty_io.c:1102 [inline]
redirected_tty_write drivers/tty/tty_io.c:1125 [inline]
redirected_tty_write+0xd4/0x120 drivers/tty/tty_io.c:1105
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (&port_lock_key){-...}-{3:3}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
_raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:166
uart_port_lock_irqsave include/linux/serial_core.h:719 [inline]
serial8250_console_write+0x177/0x1a50 drivers/tty/serial/8250/8250_port.c:3344
console_emit_next_record kernel/printk/printk.c:3183 [inline]
console_flush_one_record+0x790/0xe50 kernel/printk/printk.c:3269
console_flush_all kernel/printk/printk.c:3343 [inline]
__console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
console_unlock+0x103/0x260 kernel/printk/printk.c:3413
vprintk_emit+0x407/0x6b0 kernel/printk/printk.c:2479
_printk+0xcf/0x110 kernel/printk/printk.c:2504
register_console.cold+0xc0/0x248 kernel/printk/printk.c:4208
univ8250_console_init+0x6f/0x80 drivers/tty/serial/8250/8250_core.c:515
console_init+0x3d5/0x5b0 kernel/printk/printk.c:4407
start_kernel+0x314/0x490 init/main.c:1112
x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
x86_64_start_kernel+0x12b/0x130 arch/x86/kernel/head64.c:291
common_startup_64+0x13e/0x158
-> #0 (console_owner){....}-{0:0}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
console_trylock_spinning kernel/printk/printk.c:2026 [inline]
vprintk_emit+0x4d1/0x6b0 kernel/printk/printk.c:2478
_printk+0xcf/0x110 kernel/printk/printk.c:2504
__report_bug.cold+0x34/0x141 lib/bug.c:248
report_bug+0xb2/0x220 lib/bug.c:286
handle_bug+0x16a/0x2a0 arch/x86/kernel/traps.c:436
exc_invalid_op+0x17/0x50 arch/x86/kernel/traps.c:490
asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:593
lockdep_assert_rq_held kernel/sched/sched.h:1641 [inline]
lockdep_assert_rq_held kernel/sched/sched.h:1638 [inline]
update_rq_clock+0x40a/0xd20 kernel/sched/core.c:865
pick_next_task kernel/sched/core.c:6338 [inline]
__schedule+0x1e2d/0x6730 kernel/sched/core.c:7149
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
smpboot_thread_fn+0x893/0xaa0 kernel/smpboot.c:156
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
other info that might help us debug this:
Chain exists of:
console_owner --> &p->pi_lock --> &rq->__lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&rq->__lock);
lock(&p->pi_lock);
lock(&rq->__lock);
lock(console_owner);
*** DEADLOCK ***
1 lock held by migration/0/19:
#0: ffff88802b23b660 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:675 [inline]
#0: ffff88802b23b660 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x88/0x140 kernel/sched/core.c:659
stack backtrace:
CPU: 0 UID: 0 PID: 19 Comm: migration/0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Stopper: 0x0 <- 0x0
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
console_trylock_spinning kernel/printk/printk.c:2026 [inline]
vprintk_emit+0x4d1/0x6b0 kernel/printk/printk.c:2478
_printk+0xcf/0x110 kernel/printk/printk.c:2504
__report_bug.cold+0x34/0x141 lib/bug.c:248
report_bug+0xb2/0x220 lib/bug.c:286
handle_bug+0x16a/0x2a0 arch/x86/kernel/traps.c:436
exc_invalid_op+0x17/0x50 arch/x86/kernel/traps.c:490
asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:593
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1641 [inline]
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1638 [inline]
RIP: 0010:update_rq_clock+0x40a/0xd20 kernel/sched/core.c:865
Code: ab c8 0b 00 00 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f e9 d8 6f e6 09 a8 04 0f 84 df fc ff ff 90 0f 0b 90 e9 d6 fc ff ff 90 <0f> 0b 90 e9 92 fc ff ff 4c 8d 83 c0 0b 00 00 48 b8 00 00 00 00 00
RSP: 0018:ffffc9000045fc28 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff88802b33b600 RCX: 0000000000000001
RDX: 0000000000000046 RSI: ffffffff8e183111 RDI: ffffffff8c400a80
RBP: ffffc9000045fdd0 R08: 0000000000000001 R09: 0000000000000001
R10: ffff88806b806007 R11: 0000000bf5b29000 R12: ffffffff9122dd84
R13: ffff88802b33c4e0 R14: ffff888024812540 R15: ffff88802b23c198
pick_next_task kernel/sched/core.c:6338 [inline]
__schedule+0x1e2d/0x6730 kernel/sched/core.c:7149
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
smpboot_thread_fn+0x893/0xaa0 kernel/smpboot.c:156
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
debug_locks && !(lock_is_held(&(__rq_lockp(rq))->dep_map) != 0)
WARNING: kernel/sched/sched.h:1641 at lockdep_assert_rq_held kernel/sched/sched.h:1641 [inline], CPU#0: migration/0/19
WARNING: kernel/sched/sched.h:1641 at lockdep_assert_rq_held kernel/sched/sched.h:1638 [inline], CPU#0: migration/0/19
WARNING: kernel/sched/sched.h:1641 at update_rq_clock+0x40a/0xd20 kernel/sched/core.c:865, CPU#0: migration/0/19
Modules linked in:
CPU: 0 UID: 0 PID: 19 Comm: migration/0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Stopper: 0x0 <- 0x0
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1641 [inline]
RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1638 [inline]
RIP: 0010:update_rq_clock+0x40a/0xd20 kernel/sched/core.c:865
Code: ab c8 0b 00 00 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f e9 d8 6f e6 09 a8 04 0f 84 df fc ff ff 90 0f 0b 90 e9 d6 fc ff ff 90 <0f> 0b 90 e9 92 fc ff ff 4c 8d 83 c0 0b 00 00 48 b8 00 00 00 00 00
RSP: 0018:ffffc9000045fc28 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff88802b33b600 RCX: 0000000000000001
RDX: 0000000000000046 RSI: ffffffff8e183111 RDI: ffffffff8c400a80
RBP: ffffc9000045fdd0 R08: 0000000000000001 R09: 0000000000000001
R10: ffff88806b806007 R11: 0000000bf5b29000 R12: ffffffff9122dd84
R13: ffff88802b33c4e0 R14: ffff888024812540 R15: ffff88802b23c198
FS: 0000000000000000(0000) GS:ffff888096be1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000f73d60b8 CR3: 0000000029a59000 CR4: 0000000000352ef0
Call Trace:
<TASK>
pick_next_task kernel/sched/core.c:6338 [inline]
__schedule+0x1e2d/0x6730 kernel/sched/core.c:7149
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
smpboot_thread_fn+0x893/0xaa0 kernel/smpboot.c:156
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
---
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reply other threads:[~2026-08-02 0:07 UTC|newest]
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